The known methods of producing DL-alanine include a synthetic method making use of the Strecker reaction in which acetaldehyde, prussic acid and ammonia are used as starting materials, a production method in which a sugar is fermented by Microbacterium ammoniaphilum (JP-A-50-10028; the term "JP-A" as used herein means an "unexamined published Japanese patent application"). L-Alanine is generally produced by an enzymatic process such as a process in which L-aspartic acid is decarboxylated with an enzyme (JP-B-46-7560 corresponding to U.S. Pat. No. 3,458,400; the term "JP-B" as used herein means an "examined published Japanese patent application") or a process in which lactic acid and an amino donor is fermented by a D-alanine auxotrophic Escherichia coli strain (JP-A-62-36196), or by a process in which a sugar is fermented by Corynebacterium tumescens (JP-B-36-14298). The present inventors have also applied a process for producing L-alanine comprising fermenting a sugar by a strain belonging to the genus Arthrobacter (International Application JP91-01574 corresponding to EP-A-0 567 644). Known processes for the production of D-alanine include a process in which DL-alanineamide is hydrolyzed using a D-amidase obtained from a strain belonging to the genus Arthrobacter to form D-alanine and L-alanineamide, and the thus formed D-alanine is isolated from the reaction mixture (JP-A-1-317387 corresponding to EP-A-0 334 358) and a process in which a sugar is fermented by a D-cycloserine resistant mutant derived from Brevibacterium lactofermentum (JP-A-1-187091 corresponding to EP-A-0 310 949 and U.S. Pat. No. 5,254,464).
Further, there is a report that a small amount of alanine can be produced by recombinant DNA techniques using a strain belonging to the genus Zymomonas into which a gene coding for a Bacillus L-alanine dehydrogenase is introduced [Appl. Environ. Microbiol., 57, 1360 (1991)].
Great concern has been directed toward the development of a process for economically and industrially producing DL-alanine which is useful as a food additive, L-alanine which is useful as a food additive and a component of amino acid infusion and D-alanine which is useful in the field of pharmaceutical industry.
DL-alanine can be economically produced by chemical synthesis through the Strecker reaction, but this process is not necessarily desirable since DL-alanine is used as a food additive and, in the Strecker reaction, toxic cyanogen is used.
When optically active L- or D-alanine is required, an enzymatic or fermentation process which does not require optical resolution operation is economically advantageous in comparison with chemical synthesis processes that require such a complex operation. Fermentation processes are especially advantageous from the industrial point of view, because inexpensive sugars can be used as the starting material. Prior art processes for the fermentation production of alanine are not industrially useful because of such disadvantages as low yield and low accumulation level in the culture medium. The present inventors previously found that a microorganism belonging to the genus Arthrobacter and having reduced or deleted alanine racemase activity can ferment a sugar to produce and accumulate a significant amount of L-alanine (International Application JP91-01574). Though the yield of alanine obtained according to this method is sufficiently high, it is disadvantageous in that it requires a long period of fermentation and it is difficult to separate and purify alanine from fetid substances which are produced during the fermentation.